Most actuators have conventionally found a diversity of applications including assembling apparatus, measurement instruments, various machines, industrial robots, semiconductor manufacturing equipment and so on to drive and guide a workpiece for linear back-and-forth movement. The actuators used of late years in machinery as recited earlier have need of a high cleanliness class because they are desired to work in a controlled environment as in a clean room, in addition to conforming to growing demands for high speed operation and high acceleration/deceleration, high accuracy and compactness in construction to encourage the recently remarkable downsizing and high-functionality in electronics engineering technology.
In the commonly-assigned Japanese Laid-Open Patent Application No. 2010-138,981, referred to later as patent literature 1, there is disclosed an actuator which has an elongated frame of a U-shape in transverse section and a slider installed in the frame to move or slide lengthwise of the frame, the elongated frame and the slider being entirely made of extrusions of a light alloy which weighs less than steel. Moreover, race members, in which rolling elements run through, fit in the frames, only the race members being made of steel alloy drawn or pulled to the desired shape. As a result, the actuator is reduced in weight, smaller in height in a transverse section and slimmer in its construction. With the prior actuator constructed as stated earlier, both the frame and the slider are mainly made of extrusions of the light alloy. Mating construction between the frame and the race members has a simple structure and an upper sealing member is placed between the frame and the slider. Grooves having a T-shape in transverse section are cut on outward surfaces of side walls of the frame. The frame having a U-shape in cross section is provided on the side walls thereof with recesses having a dovetail configuration in a transverse section to fit over the race members and flanges extending to form upper edges of the recesses. The slider is also made with recesses having a rectangular shape into each of which the race member fits snugly. There is further provided a driving unit to force movement of the slider with respect to the frame.
Another actuator is described in Japanese Laid-Open Patent Application No. 2000-197,304 referred later as patent literature 2, which is composed of a housing having an opening, a slider allowed to move along the opening, and a sealing plate to close the opening. This prior actuator constructed as stated earlier is envisaged keeping debris, dust and so on, which might occur inside the actuator due to the movement of the slider, from escaping out of the actuator while excluding the contaminants, foreign materials and so on from entering the actuator. For invalidation of pumping phenomenon caused by back-and-forth movement of the slider, a hollow space is provided inside the housing to extend lengthwise in the housing and a plurality of holes on the side walls of the housing to communicate constantly at any given location between a leading compartment and a trailing compartment across the slider through the hollow space.
The prior actuator described in the patent literature 1 was unfit to work in a clean environment because the frame as shown in FIG. 1 of the patent literature 1 remains open to the surrounding atmosphere and therefore the debris and/or dirt which emanates as the slider moved is spread or diffused around. Further, the prior actuator described in the patent literature 2 was hard to maintain a high cleanliness class in various modern machines in which the slider operated with high-speed operation and/or high acceleration and/or decceleration, because of getting entirely so bulkier in volume as to need to suck or force a large amount of air inside the housing.
According to the present invention, there has been developed an improved actuator which is expected to work in the clean environment of the cleanliness class 3, higher than in the prior actuator recited earlier in the patent literature 2. The actuator of the present invention makes it possible to suck air inside the actuator and go on to cast off out of the clean room lest the debris and dirt caused by the movement of the actuator is released in the clean room.